Since the base circle diameter of gear DB is equal to 23, the value is small. If the key connection is adopted between the gear and the shaft, the strength of the shaft and the gear will be greatly reduced. Therefore, it is designed as a gear shaft. Since the driving pinion is made of 45× material and has been carburized and quenched, the shaft material is also 40Cr, which is made of carburized and quenched materials.